Materials formed on a nanometer-sized scale are being developed that provide the potential for exciting advances in optics, electronics, and chemical processing, among other applications. For instance, rare earth doped nanocrystals are of particular interest in the field of optics as the emissions, e.g., lanthanide emissions, can have a narrow linewidth emission and can possess near unity quantum efficiency. Metallic nanoparticles can find use as scatterers in optical composites and can increase rare earth emissions, can create color due to localized surface plasmon resonances, and can increase surface enhanced Raman scattering (SERS) effectiveness.
However, in order to take advantage of the potential of nano-sized materials, they need to be provided for use on a macroscopic scale without loss of desirable characteristics and at a reasonable cost. For instance, bulk nanocomposite materials have been formed using one or more polymers to form a matrix that can then encapsulate or otherwise contain the nanostructures.
Utilization of polymers has been considered to be the most desirable route to providing bulk nanocomposites as polymers can be provided with a wide variety of characteristics and as such can be tailored for specific end-use products. For instance, a polymer can be chosen for a matrix that has a Hamaker constant close to that of the nanoparticles incorporated therein. The matching of the Hamaker constants normally coincides with the matching of refractive indices and can therefore ameliorate potential dispersion and scattering problems. In addition, polymers can be processed according to a wide variety of methods and conditions and as such can be bound to nanoparticles with any of a number of linking or bridging molecules. For example, U.S. Pat. No. 6,881,490 to Kambe, et al. describes composite materials including inorganic particles at a loading level up to about 50 weight percent in which the inorganic particles are bound to the polymers forming the network by a linker molecule. Similarly, U.S. Pat. No. 7,019,082 to Matyjaszewski, et al. teaches a soft polymer network that can incorporate nanomaterials into the matrix, for instance through use of multi-branched or ‘hairy’ polymers.
Unfortunately, formation of bulk nanocomposites based upon polymeric matrices has led to problems at the macroscopic scale. Specifically, in order to be effective and of practical use, bulk nanocomposites should not detract extensively from the desirable characteristics of the individual materials of the composite, but this is a common occurrence when considering bulk nanocomposites incorporating polymeric matrices. For instance, nanostructures such as quantum dots exhibit a rapid loss of efficiency upon formation of nanocomposites with loading levels greater than about 2% by weight, and formation of nanocomposites with high loading levels of nanostructures (e.g., greater than about 50% by weight) has proven extremely difficult. Moreover, even when high loading levels have been attained, nanostructures such as rare earth doped nanocrystals suffer from agglomeration at high loading levels in bulk composites, with agglomeration resulting in undesirable scattering of light in the composite.
Attempts have been made to overcome such problems. For instance, U.S. Pat. No. 6,593,392 to Wang describes silica nanoparticles that are smaller than the desired operating wavelength. These silica nanoparticles exhibit substantially no scattering loss when bound to a fluorinated silane coupling agent that is in turn bound to a halogenated solid polymer matrix.
What are needed in the art are bulk nanocomposite materials that maintain both good optical characteristics and good mechanical and processablity properties.